Many electric arc welding devices are known and used out of doors for numerous types of operations, including light and heavy construction of buildings, vessels, manufacturing equipment, bridges, trusses, pipelines, and the like. In order to produce welds of fine quality, it is common practice to blanket the arc and the metal being welded in the immediate vicinity of the arc with an inert gas such as argon, helium, carbon dioxide and other such unreactive gases and mixtures thereof. A primary enclosure or semi-enclosure tends to direct and hold this gas around or near the arc. The purpose of such blanketing, of course, is to prevent access of atmospheric air to the arc and to the highly heated metal in its vicinity. Steels and other ferrous metals, in particular, along with other metals, including aluminum, are very susceptible to oxidation by atmospheric oxygen. Defects in welds are often produced if free access to the air is permitted. Various means are provided for maintaining a supply of the inert gas around the arc and these generally are quite satisfactory when there is no wind or other significant motion of the atmosphere around and within the equipment. For further protection of the arc and the gas blanket against winds and other strong air currents, tents of various kinds have been used but these are often unsatisfactory. Barriers of other types have often been designed or proposed. In most cases these are unwieldy and cumbersome; requiring extra manpower and consequently reducing useful production. Strong winds along or across pipelines tend to flow in a thin layer, a sort of skin effect, along or over the pipe surface and barriers which do not fit closely are often quite inadequate. The pipe is often at varying levels from the ground making it difficult to seal a tent around it. The pipe surface usually is not truly round or smooth enough that a conventional rigid barrier will give adequate protection against these surface-following air currents.
In particular, when the welding apparatus is small and of gas-shielded type, and especially if it is of orbiting or other self-propelled character, requiring close operator control for proper operation, the use of heavy tents or massive barriers as wind-breaks, and of other large protective devices is burdensome and inefficient. This sophisticated equipment is not compatible with heavy tentage and the like. It therefore has become necessary to devise secondary shrouding or shielding means of much lighter weight which (a) preferably can travel with the welding apparatus while not interfering with its operation, (b) will give good protection in detail, particularly against surface air currents, while still permitting free access by the operators to the controls and for observation of the welding operation as it proceeds, and (c) is readily adaptable to the welding apparatus without undue complexity while avoiding overloading it or its drive means. To make such equipment available is a primary object of the present invention.
While specific shielding equipment or apparatus will be described herein, with particular application to specific, known types of orbitally movable welding equipment designed especially for welding the girth joints in large diameter pipelines will be explained, it will be understood that neither the particular apparatus, shown and explained in detail, nor its special application to the very specific equipment shown, is to limit the design or utility of the invention any farther than is necessary to distinguish the invention from the prior art. The equipment has a number of variations and modifications by which it may readily be adapted by those skilled in the art, to other and wider uses.